It's about who gets the business and who holds the insurance.
In the drone world, you got established companies: DoD/Aerospace/Big Defense selling UAVs at 100K+ figures where a 15K unit can do better. And you get all these commercial startups and hobbyists are 9 out of 10 times flying with out insurance.... and if they do have insurance--how is an insurance company really going to pay out when your 2K DJI flies away and causes a car accident with million dollar lawsuits, e.g. a fatality in the middle of San Francisco's mission district? There's a reason the rocketry guys aren't flying their aerial cameras via launching the estes model unit in the local walmart parking lot.
These car sharing services, mind that all the resource sharing services (airbnb and aereo come to mind) have the same 2 problems: uneven competition (maybe fair OR unfair--courts will decide) to established businesses and regs, and when something goes wrong, who pays? You think uber has a walk in the park with safety and insurance? These are not mutually exclusive problems, but more tightly coupled than one would think.
Hence as a devil's advocate, Airports are controlled areas, congested x10, and have all sorts of complexities: emergency evac, pedestrians, basic security, basic logistics, lots of people not familiar with the area and a controlled taxi system. All that plays into the 2 above needs... and as like the drone world, safety is used as easy justification to put a kibosh on the whole deal.